1. Field of Invention
The present invention relates to an optical encoder. More particularly, the present invention relates to a transmissive optical encoder.
2. Description of Related Art
A conventional transmissive optical encoder uses an external single slit element and a lens between an optical emitter and an optical sensor to produce parallel light. FIG. 1 is a sectional view of a transmissive optical encoder according to a prior art. The transmissive optical encoder 100 has a base 110, an optical emitter 120, an optical sensor 130, a single slit element 140 and a convex lens 150.
The base 110 is a hollow casing made of an opaque substance. The base 110 has an indentation 112, several orientation elements 114, and a track 116 between two orientation elements 114.
The optical emitter 120 is on one side of the indentation 112 and the optical sensor 130 is on the other side of the indentation 112. The optical sensor 130 is set in one of track 116. And the optical emitter 120 is opposite to the optical sensor 130.
The single slit element 140 is set on the optical emitter 120 and has an opening 142 facing to the optical emitter 120. The convex lens 150 is set on the single slit element 140 and is orientated on the optical emitter 120 by an orientation part 152.
In order to limit the light emitted from the optical emitter 120, the single slit element 140 of the transmissive optical encoder 100 is set between the optical emitter 120 and the convex lens 150. Therefore, the light emitted by the optical emitter 120 passes through the opening 142 of the single slit element 140 and the convex lens 150 to the optical sensor 130. The optical sensor can receive uniform light intensity from the light source. However, the external single slit element increases the assembling difficulty and the needed materials of the transmissive optical encoder, and thus the production cost.